To the Editor: In their Clinical Review, Dr Burt and colleagues1 assessed clinical applications of adult stem cell therapies for nonmalignant diseases. They acknowledge modest benefit from hematopoietic stem cell transplantation in cardiac disease and ameliorative but noncurative outcomes in autoimmune diseases. Although we agree that greater investments are needed in the clinical development of these therapies, we disagree with the authors' suggestion that, relative to embryonic stem cells, adult stem cells provide a superior vehicle for cell-based therapies because they lack tumorigenic activity, can be prepared by methods approved by the Food and Drug Administration (FDA), and have been free of ethical controversy. It would have been more appropriate to note that their review targeted hematopoietic stem cell transplantation because embryonic stem cells are not yet ready for clinical use.